Method and a Device for Total Spinal Disc Replacement

ABSTRACT

A method for total replacement of an affected intervertebral disc through a dorsal approach comprising the steps of removing the disc material of the affected intervertebral disc ( 3 ) and inserting an intervertebral prosthesis ( 30 ) into the intervertebral disc space via an extraforaminal path ( 23 ). An intervertebral prosthesis ( 100 ), in particular an intervertebral disk prosthesis comprising A) a first prosthetic component ( 101 ) having a first apposition surface ( 107 ) disposed transversely to the central axis ( 103 ) B) a second prosthetic component ( 102 ) having a second apposition surface ( 108 ) disposed transversely to the central axis ( 103 ); whereby C) said first and second prosthetic components ( 101;102 ) are connected by means of an articulation ( 106 ); whereby D) when viewed parallel to said central axis ( 103 ) said first and second prosthetic components ( 101;102 ) have an elongated shape with a major axis ( 127 ) and a transverse minor axis ( 128 ); E) said central axis ( 103 ), major axis ( 127 ) and transverse minor axis ( 128 ) intersecting each other and said central axis ( 103 ) and transverse minor axis ( 128 ) defining a middle plane ( 126 ); F) said first and second prosthetic component ( 101;102 ) have a cross-sectional area orthogonal to said central axis ( 103 ) which is essentially oval or elliptical; whereby G) said cross-sectional area comprises at least two concavities ( 125;130 ) lying on different sides of said middle plane ( 126 ) and on the same side of said major axis ( 127 ).

Today the state of the art concerning total spinal disc replacement device insertion is the anterior approach, i.e. true anterior, anterolateral (oblique) or true lateral. The surgeon decides between transperitoneal or retroperitoneal approaches, depending on the treated level or his personal experience. However, due to the presence of major vessels (e.g. aorta, vena cava) the anterior approach to the spine is often performed in the presence of vascular surgeons thereby causing extra costs.

In U.S. Pat. No. 6,719,794 GERBER a method for insertion of an intervertebral fusion implant is disclosed. The removal of the affected spinal disc as well as the insertion of the implant is performed via a posterior approach offset from the midline of the spine to the affected intervertebral disc. Disadvantageously, such a transforaminal approach includes a partial dissection of the facet joint.

A prosthetic device for transforaminal insertion into an intervertebral space is known from US 2004/0225365 EISERMANN. This known prosthesis comprises two components having an articulating surface each in order to permit articulating motion between the first and second components and consequently of the adjoining vertebrae. The transforaminal path disclosed might cause potential damage to important anatomical structures such as nerve roots, dura, ligamentum flavum and interspinous ligaments.

Therefore, it is an object of the present invention to provide a method for total spinal disc replacement device insertion including a dorsal approach to the spine without having to dissect the facet joint neither completely nor partially.

According to the method of the present invention the above object is achieved by means of an extraforaminal approach including an access portal in the Fibrocartilago Intervertebralis between the anterior and posterior longitudinal ligaments for removing the affected intervertebral disc as well as for insertion of a total disc prosthesis.

The method according to the invention offers the following specific advantages:

-   -   A wide opening to the intervertebral space compared to true         posterior or transforaminal approaches is achievable;     -   The surgeon passes the neural structures and does not have to         dissect the facet joint;     -   The detection of the correct trajectory can be made with a         visualisation of the Processus Transversus;     -   The patient is in prone position as he would be for dorsal         fixation procedures; and     -   The surgeon is used to patient positioning and incisions.

In a preferred embodiment the key element of the extraforaminal approach to the spinal disc is a path in front of the transverse processes (Processus Transversus).

In a further embodiment the method further comprises the steps of:

A) Performing a dorsal incision extra-medially, i.e. apart from the median longitudinal plane by targeting the Fascia Lumbodorsalis; B) Approaching the affected intervertebral disc with a Kirschner wire; C) Inserting along the Kirschner wire a trocar and a protection sleeve to the affected intervertebral disc; D) Cutting out an access portal of a width W and an area A into the Fibrocartilago Intervertebralis with a cutting instrument; E) Removing the disc material with a surgical device; F) Cleaning the endplates of the adjacent upper and lower vertebral body with a surgical device; G) Opening or enlarging of the intervertebral space by using a distractor; H) Inserting an intervertebral prosthesis through the access portal by means of an implant holder.

In another embodiment the disc material is removed with a surgical device through a protection sleeve. This permits the advantage that the use of a protection sleeve during removing the disc material allows a better protection of the surrounding soft tissue.

In a further embodiment the access portal is cut at a distance X>0 apart from the anterior longitudinal ligament and the posterior longitudinal ligament, therewith permitting the advantage that the anterior longitudinal ligament and the posterior longitudinal ligament remain intact in order to stabilize the treated segment of the vertebra.

In still another embodiment the distance X amounts between 2 mm and 38 mm.

In a further embodiment the width W of the access portal is between 8 mm and 36 mm.

In still a further embodiment the area A of the access portal is between 24 mm² and 684 mm² and the height is preferably between 3 and 19 mm.

In another embodiment the step of distracting of the vertebral bodies adjoining the disc space to be treated is performed through the protection sleeve.

In a further embodiment the distraction of the vertebral bodies adjoining the disc space to be treated is performed by slightly bending a distractor in order to keep the view to the situs free for the surgeon.

In yet a further embodiment the total disc replacement procedure is performed without dissecting the facet joints.

In another embodiment the total disc replacement procedure is performed without dissecting the transverse processes.

In a further embodiment the access to the intervertebral space to be treated is essentially straight. This allows the advantage that due to the almost straight access the use of essentially straight instruments e.g. for cleaning the endplates of the adjacent vertebral bodies or other surgical actions is possible.

In another embodiment the incision is reduced to a tube.

In a further embodiment the risk of damaging the neural structures is reduced by means of passing (not approaching) the spinal cord and locating, mobilising and marking the nerve root.

It is a further object of the invention to provide an intervertebral prosthesis having a contour when viewed orthogonally to its central axis which has a minimal width but still an adequate articulation area.

According to the invention the above object is achieved through an intervertebral prosthesis which essentially comprises a first and a second prosthetic component each having an apposition surface disposed transversely to the central axis and apt for contacting the end plate of an adjoining vertebral body each. Furthermore, said first and second prosthetic components are connected by means of an articulation. When viewed parallel to said central axis said first and second prosthetic components have an elongated shape with a major axis and a transverse minor axis, whereby said central axis, major axis and transverse minor axis intersect each other and said central axis and transverse minor axis defining a middle plane. Said first and second prosthetic component have a cross-sectional area orthogonal to said central axis which is essentially oval or elliptical and said cross-sectional area comprises at least a first and a second concavity lying on different side of the middle plane and on the same side of the major axis.

The intervertebral prosthesis according to the invention offers the following specific advantages:

-   -   the first and second prosthetic components have a small width at         their portions towards their lateral ends but still an adequate         width adjacent the middle plane where the articulation is         located, said small width allowing an implantation by means of         an extraforaminal access and said adequate width adjacent the         middle plane allowing the configuration of an articulation         adapted to the natural intervertebral disc;     -   un-necessary material on the first and second prosthetic         components (bone contact plates) is removed in order to give         special attention to the fact that the bony endplates of the         vertebral bodies change their shape at the location where the         prosthesis is situated during their degeneration, i.e. they         become more undulated over time; and     -   possible osteophytes on the posterior periphery of the vertebral         endplates which the surgeon decides not to remove are taken into         consideration, i.e. the intervertebral prosthesis can be         positioned easier because the prosthesis can be manipulated         around the undulations.

In a preferred embodiment of the intervertebral prosthesis said cross-sectional area of said first and second prosthetic component is kidney shaped with an enlargement arranged essentially symmetrical to said the middle plane.

In a further embodiment said at least two concavities have an essentially semi-elliptical or semi-oval shape.

In another embodiment said at least two convavities are disposed essentially symmetrical to said middle plane.

In still another embodiment said first and second prosthetic component have a length H measured parallel to said major axis and wherein each of said at least two concavities has a width W measured parallel to said major axis, said width W amounting to between 15% and 35% of said length H.

In yet another embodiment said first and second prosthetic component have a maximum width B measured parallel to said transverse minor axis and wherein each of said at least two concavities has a depth T measured parallel to said transverse minor axis, said depth T amounting to between 5% and 25% of said maximum width B.

In a further embodiment said cross-sectional area of said first and second prosthetic components has an essentially elliptical periphery with a smaller radius of curvature at the first subsidiary vertex than at the second subsidiary vertex of said periphery.

In another embodiment said first subsidiary vertex is on the same side of said major axis as said at least two concavities.

In a further embodiment, the ratio of the length H of the prosthetic components to the width B thereof is between 3:1 and 5:1. The advantage of this design essentially is that in order to implant the two prosthetic components in the intervertebral space (intervertebral disk) it is only necessary to clear a narrow access path such permitting an extraforaminal approach.

In yet a further embodiment said articulation is configured as a ball-and-socket joint comprising a spherical cap connected to one of the first and second prosthetic components and congruent to said spherical cap a spherical recess in the other of said first and second prosthetic components.

In another embodiment, the intervertebral prosthesis is realised in two pieces, i.e. the spherical cap is made in one piece with one of the two prosthetic components.

In a further embodiment, the intervertebral prosthesis is realised in three pieces, so that the spherical cap forming the third piece is connectable with one of the two prosthetic components. The advantage of this design is to be seen essentially in the fact that the plate and the spherical cap may be realised by using different materials, so that it is possible to achieve optimal sliding properties for the articular surfaces. Preferred materials for the plates are titanium or a titanium alloy as well as PEEK or coated variants, and for the spherical cap highly crosslinked polyethylene (X-UHMWPE), an alloy of cobalt and chrome, or a ceramic material.

In again a further embodiment, the intervertebral prosthesis is realised in at least three pieces and comprises an articular shell including the recess, whereby said articular shell is attachable to one of said first and second prosthetic components as a third piece. The advantage of this design is to be seen essentially in the fact that the plate and the spherical cap may be realised using different materials, so that it is possible to achieve optimal sliding properties for the articular surfaces.

In a further embodiment, the spherical cap and the articular shell consist of a material combination made of metal and plastic. The advantages of this embodiment are that it is possible to use proven combinations of joint replacement materials such as, for example, highly crosslinked polyethylene (X-UHMWPE) and an alloy of cobalt and chrome. Further advantages are to be seen in the fact that low frictional forces are achievable for the relative displacement of the articular surfaces and that a compensation of axial impact loads can be achieved.

In yet another embodiment a ceramic-to-ceramic articulation is used. In a further embodiment the surfaces of the spherical cap and the recess are coated with titanium carbide or with amorphous carbon (ADLC) therewith permitting a substantial reduction of the coefficient of friction.

In another embodiment, at least the spherical cap is made of a memory metal or of a material capable of swelling (e.g. hydrogels). In still another embodiment at least the spherical cap is made of a flowable, thermosetting material. The monomers, comonomers, homopolymers, oligomers, or mixtures which contain such thermosetting, flowable substances may suitably be selected from the group of:

a) polyethylene glycols, preferably polyethylene glycol(di)-acrylates; b) n-vinylpyrrolidones; and c) vinyls, preferably vinyl alcohols; and d) styrenes.

The polymers thus obtained may be widely varied as regards their elasticity. The advantages of these designs are to be seen essentially in the fact that due to the reduced volume of the joint, the insertion of the intervertebral prosthesis becomes less invasive, the increased volume being best suited for achieving an optimal articular function.

In a further embodiment the first prosthetic component is selected from a first kit of at least M≧2 first prosthetic components and the second prosthetic component is selected from a second kit of at least N≧2 second prosthetic components. Said first and second kit may comprise first and second prosthetic components being provided with different heights, articulation radii or locations of the centre of the respective radii, i.e. the center of rotation. By means of this embodiment the following advantages may be achieved:

-   -   the position of the centre of rotation is adjustable in height         as the two component parts may be arranged in a modular manner;     -   the components which may also vary in the radius of the         spherical cap, which makes it possible to adjust the centre of         rotation of the intervertebral prosthesis;     -   the position of the centre of rotation, the angulation, and the         portion of translatory motion of the intervertebral prosthesis         may be freely selected within a relatively wide range, the         portion of translatory motion being the portion of movement         measured transversely to the central axis of the prosthetic         components relative to each other;     -   the prosthetic components may also take into account the         articulation requirements of the motion segment in that it is         possible to include spherical caps having different radiuses.         Greater spherical cap radiuses have a higher portion of         translatory motion during deflection, which on the flexion of a         patient's spine puts increased pressure on the facet joints and         leads to an accelerated degeneration thereof;     -   the heights of the prosthetic components and the corresponding         radiuses of the articulating spherical cap of the intervertebral         prosthesis may vary and are thus adaptable to the dimensions of         different intervertebral spaces.

In yet a further embodiment said first and second prosthetic component each comprise an intermediate surface, said first and second intermediate surfaces facing each other. At least the first or second intermediate surface is provided with at least one cavity with an undercut being located at the first or/and second lateral end of said first and second prosthetic components, said cavity with an undercut being apt for acceptance of an anchoring member of an implant holder.

The implant holder according to the invention is provided with a sleeve and an anchoring member, e.g. a hook member being insertable into the cavity and undercut and being displaceably disposed in the central bore of the sleeve, said implant holder further having a front end being provided with a fore-part which is adapted to the lateral ends of the first and/or second prosthetic component of an intervertebral prosthesis according to invention. Furthermore, the implant holder is provided with a fastening mechanism permitting to pull the anchoring member towards the sleeve such pressing the lateral end of the intervertebral prosthesis against the fore-part.

Further objects and advantages of the invention will become apparent from the following description when read with reference to the accompanying drawings which illustrate the method according to the invention. In the drawings:

FIG. 1 is a cross-section through the spinal column orthogonal to the longitudinal axis of the spinal column;

FIG. 2 is a plane view to the back of a patient in prone position;

FIG. 3 is a plane view to the dorsal muscle configuration of a patient;

FIG. 4 is a cross-section through the body of a patient orthogonal to the longitudinal axis of the spinal column and seen from cranial;

FIG. 5 is a perspective view to the lumbar part of the spinal column whereby a Kirschner wire is inserted into the affected spinal disc according to one step of an embodiment of the method of the present invention;

FIG. 6 is a perspective view to the lumbar part of the spinal column whereby a trockar and a protection sleeve are slid over the Kirschner wire according to one step of an embodiment of the method of the present invention;

FIG. 7 is a perspective view to the lumbar part of the spinal column whereby a cutting device is slid through the protection sleeve according to one step of an embodiment of the method of the present invention;

FIG. 8 is a perspective view to the lumbar part of the spinal column whereby an access portal is being cut into the affected disc space;

FIG. 9 is a perspective view to the lumbar part of the spinal column together with a distractor according to one step of an embodiment of the method of the present invention;

FIG. 10 is a perspective view to the lumbar part of the spinal column together with an intervertebral prosthesis and an implant holder according to one step of an embodiment of the method of the present invention;

FIG. 11 is a lateral view to the portion of the spinal column together with the inserted intervertebral prosthesis;

FIG. 12 is a view from anterior to the portion of the spinal column together with the inserted intervertebral prosthesis;

FIG. 13 is a top view of an embodiment of the intervertebral prosthesis according to the invention;

FIG. 14 is a front view of the embodiment of FIG. 13;

FIG. 15 is a lateral view of the embodiment of FIGS. 13 and 14;

FIG. 16 is a perspective view of the second prosthetic component of the embodiment of FIGS. 13-15;

FIG. 17 is a cross-section along the major axis of the second prosthetic component of FIG. 16;

FIG. 18 is a magnified view of one lateral end of the second prosthetic component of FIGS. 16 and 17;

FIG. 19 is a perspective view of the second prosthetic component of FIGS. 16-18 together with the leading end of an embodiment of the implant holder according to the invention; and

FIG. 20 is a perspective view of the second prosthetic component of FIGS. 16-18 together with a portion of the sleeve of an embodiment of the implant holder according to the invention.

Description of the preferred method for replacement of a spinal disc through an extraforaminal approach according to the invention:

-   1. Performing a dorsal incision 12 approximately 7 cm extra-medial,     i.e. apart from the median longitudinal plane 2 whereby the Fascia     Lumbodorsalis is targeted in order to minimize the muscular     destruction (FIG. 3); -   2. Approaching the affected intervertebral disc 3 with a Kirschner     wire 14 in an extraforaminal path 23 in front of the processus     transversus 6 whereby the use of X-ray control, e.g. an image     intensifier is mandatory (FIG. 5); -   3. Inserting along the Kirschner wire 14 a trockar 15 and a     protection sleeve 16 to the affected intervertebral disc 3 passing     the Processus Costalis 17 (FIG. 6); -   4. Cutting an access portal 9 of a width W and a height H (FIG. 8)     into the Fibrocartilago intervertebralis 18 apart from the anterior     longitudinal ligament 5 (FIG. 1) and the posterior longitudinal     ligament 4 (FIG. 1) with a cutting instrument 19 (FIG. 7); -   5. Removing the disc material with curettes, rongeurs, spoons lead     through the protection sleeve 16, preferably with use of an     endoscope; -   6. Cleaning the endplates of the adjacent upper and lower vertebral     body 10;11, particularly by use of specific instruments like water     jet or ultrasonic devices, preferably with use of an endoscope; -   7. Removing the affected intervertebral disc 3 by slightly bending a     distractor 20 in order to keep the view to the situs free for the     surgeon, whereby the distraction is performed through the protection     sleeve 16 (FIG. 6) or a soft tissue retractor (FIG. 9); -   8. Inserting the intervertebral prosthesis 30 through the access     portal 9 by means of an implant holder 22 whereby the use of X-ray     control, e.g. an image intensifier in order to control the position     of the intervertebral prosthesis 30 is mandatory (FIG. 10).

A detailed description of an extraforaminal approach to vertebral bodies in case of posterolateral fusion of vertebrae, e.g. by securing bone grafts to the pedicles or transverse processes by means of bone screws can be found in:

Watkins Melvin B. “Posterolateral fusion of the lumbar and lumbosacral spine” J Bone Joint Surg Am. 1953 October; 35-A(4):1014-8 Watkins Melvin B. “Posterolateral fusion in pseudoarthrosis and posterior element defects of the lumbosacral spine” Clin Orthop Relat Res. 1964 July-August; 35:80-5.

FIGS. 11 and 12 illustrate the situation after completion of the surgical process, i.e. an intervertebral prosthesis 30 has been inserted between the two vertebral bodies 10;11. The intervertebral prosthesis 30 shown comprises an upper and a lower apposition member 24;25 the outer surfaces of which abut the end plates of the vertebral bodies 10; 11. Furthermore, the intervertebral prosthesis 30 comprises an articulation 26 jointedly connecting the upper and lower apposition member 24;25 such allowing articulating motion between the two apposition members 24;25 and consequently of the two adjoining vertebrae 10;11.

FIGS. 13-15 illustrate an embodiment of the intervertebral prosthesis 100 comprising a first prosthetic component 101, a second prosthetic component 102 and an articulation 106 articulatedly connecting said first and second prosthetic component 101;102. Opposite said articulation 106 the first and second prosthetic component 101;102 comprise a first apposition surface 107, respectively a second apposition surface 108, whereby said first apposition surface 107 is configured for abutting the base plate of a first intervertebral body 10 contacting the intervertebral prosthesis 100 on top and said second apposition surface 108 is configured for abutting the cover plate of a second intervertebral body 11 contacting the intervertebral prosthesis 100 at the bottom. The articulation 106 is configured as a ball-and-socket joint, said ball-and-socket joint comprising a spherical cap 112 at the second prosthetic component 102 and congruent to said spherical cap 112 a spherical recess 111 in the first prosthetic component 101.

Each of the first and second apposition surfaces 108;109 is disposed transversely to the central axis 103. When viewed parallel to said central axis 103 said first and second prosthetic components 101;102 have an elongated shape with a major axis 127 and a transverse minor axis 128, whereby said central axis 103, major axis 127 and transverse minor axis 128 intersect each other. Said central axis 103 and said transverse minor axis 128 further define a middle plane 126. Furthermore, said first and second prosthetic component 101;102 have a cross-sectional area orthogonal to said central axis 103 which is essentially elliptical and comprises two concavities 125 lying on different sides of said middle plane 126 and on the same side of said major axis 127.

The two concavities 125 are disposed symmetrically to said middle plane 126 such that one of said two concavities 125 is arranged in a first quadrant of a circle the centre of which coincides with the point of intersection of the major axis 127, the transverse minor axis 128 and the central axis 103 and the circumference of which is tangent to the periphery 129 of said cross-sectional area at the principal vertices. The second of said two concavities 125 is arranged in a clockwise succeeding, second quadrant of said circle. Furthermore, the two concavities 125 have an essentially semi-elliptical shape and have a depth T measured parallel to said transverse minor axis 128 amounting to about 5% of the maximum width B of said first and second prosthetic components 101;102.

The first and second prosthetic component 101;102 each comprise an intermediate surface 109; 110, said first and second intermediate surfaces 109; 110 facing each other. As shown in FIGS. 16-18 the second intermediate surface 110 is provided with two cavities 131 with an undercut 132 being located at the first and second lateral end 133;134 of said first and second prosthetic components 101;102 whereby said cavities 131 with undercut 132 are apt for acceptance of an anchoring member 141 of an implant holder 22 (FIG. 19,20) whereby the surgeon may select the respective cavity 133 in case of approaching the intervertebral space from the left or from the right side.

FIGS. 19 and 20 illustrate an embodiment of the implant holder 22 which is provided with a sleeve 140 and an anchoring member 141, with a hook member at the front end. The anchoring member 141 may be inserted into the cavity 131 and undercut 132 and is displaceably disposed in the central bore of the sleeve 140. The implant holder 22 further has a front end 142 being provided with a fore-part 143 which is adapted to the lateral ends 133,134 (FIG. 16) of the first and/or second prosthetic component 101,102. Furthermore, the implant holder 22 is provided with a fastening mechanism (not shown) permitting to pull the anchoring member 141 into the sleeve 140 such pressing the lateral end 133 of the intervertebral prosthesis against the fore-part 143. The sleeve 140 is curved in order to permit an insertion of the intervertebral prosthesis 100 along an extraforaminal path. 

1-15. (canceled)
 16. An intervertebral prosthesis comprising; a first prosthetic component having a first surface disposed transversely to a central axis for contacting the end plate of a first adjoining vertebral body and further comprising a first cross-sectional area which is orthogonal to a central axis and elliptical in shape; a second prosthetic component having a second surface disposed transversely to the central axis for contacting the end plate of a second adjoining vertebral body and further comprising a second cross-sectional area which is orthogonal to the central axis and elliptical in shape; wherein: said first and second prosthetic components are connected by means of an articulation; wherein said first and said second prosthetic components each have an elongated shape with a major axis and a transverse minor axis when viewed parallel to the central axis; and said central axis, major axis and transverse minor axis intersect each other and said central axis and said transverse minor axis defining a middle plane; whereby said first and second cross-sectional areas comprise at least two concavities on different sides of said middle plane and on the same side of said major axis.
 17. The intervertebral prosthesis as claimed in claim 1, wherein said first cross-sectional area and said second cross-sectional area are kidney shaped with an enlargement arranged essentially symmetrical to said middle plane.
 18. The intervertebral prosthesis as claimed in claim 1, wherein said at least two concavities have an essentially semi-elliptical or semi-oval shape.
 19. The intervertebral prosthesis as claimed in claim 1, wherein said at least two concavities are disposed essentially symmetrical to said middle plane.
 20. The intervertebral prosthesis as claimed in claim 1, wherein said first and second prosthetic component has a length measured parallel to said major axis and wherein each of said at least two concavities has a width measured parallel to said major axis, said width amounting to between fifteen percent and thirty-five percent of said length.
 21. The intervertebral prosthesis as claimed in claim 1, wherein said first and second prosthetic component has a maximum width measured parallel to said transverse minor axis and wherein each of said at least two concavities has a depth measured parallel to said transverse minor axis, said depth amounting to between three percent and twenty-five percent of said maximum width.
 22. The intervertebral prosthesis as claimed in claim 1, wherein said first cross-sectional area and said second cross-sectional area have an essentially elliptical periphery with a smaller radius of curvature at the first subsidiary vertex than at the second subsidiary vertex of said periphery.
 23. The intervertebral prosthesis as claimed in claim 1, wherein said first subsidiary vertex is on the same side of said major axis as said at least two concavities.
 24. The intervertebral prosthesis as claimed in claim 1, wherein said first and second prosthetic components have a length measured parallel to said major axis and a maximum width measured parallel to said transverse minor axis, wherein the ratio of the length to the maximum width is between 3:1 and 5:1.
 25. An intervertebral prosthesis comprising: a first prosthetic component having a first surface disposed transversely to a central axis for contacting the end plate of a first adjoining vertebral body and further comprising a first cross-sectional area which is orthogonal to a central axis and elliptical in shape; a second prosthetic component having a second surface disposed transversely to the central axis for contacting the end plate of a second adjoining vertebral body and further comprising a second cross-sectional area which is orthogonal to the central axis and elliptical in shape; wherein: said first and second prosthetic components are connected by means of an articulation wherein said articulation is configured as a ball-and-socket joint comprising: a spherical cap connected to one of the first and second prosthetic components and a spherical recess congruent to said spherical cap in the other of said first and second prosthetic components.
 26. The intervertebral prosthesis as claimed in claim 10, wherein one of the first and second prosthetic components and the spherical cap consist of a single piece.
 27. The intervertebral prosthesis as claimed in claim 10, wherein said intervertebral prosthesis comprises at least three pieces with the spherical cap being the third piece attachable to one of said first and second prosthetic components.
 28. The intervertebral prosthesis as claimed in claim 12, wherein said intervertebral prosthesis further comprises an articular shell including a recess which is attachable to one of said first and second prosthetic components as the third piece.
 29. The intervertebral prosthesis as claimed in claim 13, wherein the spherical cap and the articular shell consist of a material comprising metal and plastic.
 30. The intervertebral prosthesis as claimed in claim 13, wherein the spherical cap and the articular shell consist of a ceramic-to-ceramic material pairing.
 31. The intervertebral prosthesis as claimed in claim 13, wherein the surfaces of the spherical cap and of the recess are coated with titanium carbide or with amorphous carbon.
 32. The intervertebral prosthesis as claimed in claim 10, wherein at least the spherical cap is made of a memory metal.
 33. The intervertebral prosthesis as claimed in claim 10, wherein at least the spherical cap is made of a material capable of swelling.
 34. The intervertebral prosthesis as claimed in any one of the claims 10, wherein at least the spherical cap is made of a flowable, thermosetting material.
 35. The intervertebral prosthesis as claimed in claim 10, wherein at least the spherical cap is made of a monomer, comonomer, homopolymer, oligomer, or mixtures which contains a thermosetting, flowable substance.
 36. The intervertebral prosthesis as claimed in claim 20, wherein the thermosetting, flowable substance is selected from the group of: a) polyethylene glycols; b) n-vinylpyrrolidones; c) vinyls; and d) styrenes.
 37. The intervertebral prosthesis as claimed in claim 1 wherein said first prosthetic component is selected from a first group of at least two first prosthetic components.
 38. The intervertebral prosthesis as claimed in claim 1, wherein said second prosthetic component is selected from a second group of at least two second prosthetic components.
 39. The intervertebral prosthesis as claimed in claim 1, wherein said first and second prosthetic component each comprise an intermediate surface, said first and second intermediate surfaces facing each other and at least the first intermediate surface being provided with at least one cavity with an undercut being located at a first lateral end of said first and second prosthetic components and being capable of accepting an anchoring member of an implant holder.
 40. (canceled) 